The present invention concerns a system for making an optical lens from a blank.
Prior art systems of the above type include systems which include a device for applying an adapter to the blank for transferring it into and mounting it in a device for trimming it, in accordance with trimming information, to make the optical lens.
An optical lens blank is held between two ends of a split shaft of a grinding machine by an adapter in the form of a suction device or any kind of adhesive support, for example, applied accurately to the blank to define its rotation axis in the grinding machine.
Centering the adapter on the blank is a relatively complex operation that must be carried out allowing for various factors.
The accuracy of the centering operation conditions correct trimming of the blank and the best possible matching of the resulting lens to its environment, i.e. the patient by whom the lens and the frame supporting it will be worn.
Using electronic systems to control grinding machines by means of databases or databanks containing the specifications of various eyeglass frames or by means of a device including feeler means for feeling a frame in which the lens is to be fitted or a corresponding template is already known in itself.
The feeler means are adapted to measure radii of a frame or of a corresponding template that are then used to generate control signals applied to the grinding machine by means of a computer when the blank is trimmed to obtain the lens.
A computer of the above kind is generally associated with a screen for displaying the shape of the rims of the frame or that of the template for checking by the user of the system.
Reference may be had to document EP-A-0 092 364, for example, and to document FR-A-2 547 930 which are particularly concerned with a numerically controlled grinding machine.
However, the methods and devices described in the above documents still have the drawback of necessitating very accurate centering of the adapter on the lens blank in accordance with marks previously made on it.
One attempt to solve this problem is described in document EP-A-0 206 860 which describes a device for accurately centering an adapter on and applying an adapter to an optical lens blank.
The device determines for itself the information it needs for direct control of the trimmings machine in accordance with specific morphological data of the patient by whom the glasses will be worn and data relating to the selected frame.
The device described in the above document includes a frame database or databank and a computer with an associated display screen, for example a flat electronic display.
The computer also includes means for displaying and moving on the screen an image stored in the databank of an eyeglass frame or a corresponding template and means for commanding and storing movements of the image of the frame on the screen, means for calculating the differences between its final coordinates and a reference position and calculating control information for the grinding machine therefrom, and means for applying corresponding commands directly to the grinding machine in order to trim the blank.
Finally, the device described in the above document includes a pivoting system for applying the adapter to the blank and optical aiming means for positioning the blank under the pivoting system for applying the adapter.
However, before the trimming can be done the user of the above device still needs to verify the characteristics of the blank, for example its optical power, and to mark on it its optical center, for example, and in the case of a cylindrical blank its optical axis or other optical characteristics depending on the type of blank and the type of lens to be made.
The skilled person usually refers to these various operations as checking and pricking or marking the blank.
The checking and marking operations can be carried out independently of the other operations that have just been described using a self-contained measuring device such as a projection focometer which can be used to determine the optical characteristics of the blank, for example the sphere and cylinder values, the addition and the orientation of the optical axis or other axes of the blank.
Also, means for marking the position of the axis or axes are also needed, such means comprising, for example, graphical means such as ink spots or stamps, etc.
This also has a disadvantage, however, in that apart from the fact that the devices are relatively costly and bulky, they are independent of the other means of preparing for trimming the blank and necessitate moving the blank between various workstations on the device.
This leads to a high risk of errors in centering of the adapter on the blank during the various operations described previously because of maladjustment or wear of the various devices described or because of human error, directly related to the user of the devices, in which case the errors are cumulative and may lead to a serious defect in the positioning of the adapter on the blank.
The consequence of this is a defective lens that is not matched to the characteristics of the wearer.